2019 XC-60 T-5 AWd Fuel requirement

If this has been talked about, could someone post a link to it? But the dealer says that the T-5 uses regular , 87 octane fuel (US), but that the T-6 and T-8s need 91 octane as they are supercharged . He even printed it out for me. But the manual and sticker on the fuel door say 91 octane. He says that those are recommendations from Volvo on the T-5. Anyone one have a better handle on which octane is required ? I know I can always go to 91, but if 87 works, that will save some money at the pump.
By the way, getting 21.5 MPG...is that pretty typical for the T-5?

Here you go.... if you put in regular fuel anything less than 91, the electronics (ECM) will adjust your motor's tuning to run the fuel without knocking. Some of you may remember the pinging sound. This is called detonation or knocking and is bad for a motor. To prevent this, the motor has KNOCK sensors that adjust the burning of the fuel (timing) so there is no ping/knock. In doing so your car is less efficient. Your MPG will drop 10-20% and you will have even less power. So you just saved $$ at the pump but as a result you go to the pump more often. so there is no savings and your wonderfully under-powered Volvo is even more under-powered.